The primary disadvantage in using barbells involves considerations of safety. For this reason a variety of weight training machines have been developed, as they provide a degree of safety that barbells presently do not provide. This safety factor is documented in a Sports Illustrated (trademark) publication entitled STRENGTH TRAINING Your Ultimate Weight Conditioning Program by John Garhammer on page 48;
"As for safety, machines have some advantages over free weights. You can fall with a barbell, drop a dumbbell on yourself, or get stuck underneath a barbell when performing the bench press. These kinds of accidents should not happen if you use proper technique in your free weight exercises, handle reasonable weights, and use "spotters" during exercises such as the squat and bench press. But if you're not careful, these kinds of accidents can happen with free weights, while they're unlikely or impossible with machines."
Exercise machines tend to be more expensive than barbells, so many persons workout with barbells notwithstanding the potential for accidents. Invariably persons who have not mastered the proper techniques attempt barbell workouts when "spotters" are not available, so accidents involving barbells continue to occur.